Ion Mobility Spectroscopy (IMS) is used to determine the composition of sample gases through time-of-flight analysis of their constituent ions. In order to accomplish this, neutral atoms of sample gases are subjected to an ionization process that includes direct bombardment by energetic electrons causing secondary electron liberation from neutral atoms or molecules and creation of primary positive (+) ions; attachment of low energy electrons to neutral atoms or molecules creating (−) ions; chemical reactions and charge exchange between ions and neutral atoms or molecules; attachment of ions to neutral atoms or molecules; and recombination processes between charged particles. After the composition of ions has stabilized, the ions are gated into the drift region of a drift tube at regular intervals using a homogenous electric field. Once inside the drift region, their different mobilities and resultant chemical identities are determined based on their ion charge, ion mass and ion shape.